Windows: More RDR Garbage Collection

This patchset addresses the failure of AFSVolumeCB, AFSDirectoryCB,
and AFSObjectInformationCB objects to be garbage collected by the
AFSPrimaryVolumeWorker thread.  The AFSPrimaryVolumeWorker thread
is broken up into smaller pieces.

Change-Id: I54749960be8f22313ba7ee5f9f96438be6321f25
Reviewed-on: http://gerrit.openafs.org/8995
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>